Referring to FIG. for illustrating a conventional electro-photography process unit, the surface of a photo-sensitive drum 28 is uniformly charged with a constant voltage electric charger 25 and then exposed to the light of a lamp 24 reflected from an original document placed on a platen glass 21, so that an electrostatic latent image is formed on the photo-sensitive drum 28 corresponding to the image of the document. The light source may be a laser scanning unit, light emitting diode, etc. Thereafter, as the photo-sensitive drum 28 is rotated, the toner of a developer 27 is attracted to the surface of the photo-sensitive drum 28 so as to develop the latent,. image transferred by a transfer means 32 to a sheet of paper 31 supplied by a supply roll 20.
The paper adhering to the photo-sensitive drum 28 by the electrostatic force is separated by a separator 33 therefrom. Then the paper is conveyed by a conveyor belt 30 to a fixing means 40, where the paper is heated and pressed between a heat roll 34 and pressure roll 35 to fix the toner, conveyed to a discharging tray 39.
The residual toner on the photo-sensitive drum 28 is removed by a cleaning blade 29 and the latent image is canceled by the light supplied from a pre-erase lamp array 37.
Referring to FIGS. 3A and 3B, the rotation of the drum 28 is preformed by the rotational force of the drive gear 22 of a motor being transmitted via an idle gear 23 to a drum gear 28a mounted on one end of the shaft of the drum 28. The developer 27 arranged in one side of the drum 28 has a sleeve 27b with a sleeve gear 27a that is driven by the drum gear 28a to rotate the magnet roll of the developer. On the opposite side of the drum with respect to the developer 27, is arranged the cleaning blade 29 attached by means of a fixing pin inserted in a slot formed in the base. The cleaning blade 29 has a cleaning roll 29b whose shaft has at one end a cleaning gear 29a engaged with the drum gear 29a.
Such a conventional drive system has a drawback that the gaps between the drum 28 and sleeve 27b and cleaning blade 29 are not kept constant as shown in FIG. 3A because the shaft of the drum 28 receives the torque of the drum gear 28a only at one end so that the relative positions of the drum, sleeve and cleaning blade are deviated from their original positions during the operation.